1. Field of the Invention
This invention relates to an anti-seismic device, and more particularly to an anti-seismic device that includes a plurality of vibration-reducing units which are arranged in parallel.
2. Description of the Related Art
In a tuned mass damping system, a mass is suspended from a building structure by a steel cable so as to diminish oscillations in the building structure. By correctly matching the mass with the relevant parameters of the building structure, the mass can oscillate in a direction opposite to that of the oscillation direction of the building so as to absorb the vibration energy of the building structure.
The aforesaid mass damping system suffers from the following disadvantages:                (1) When errors occur in evaluation of the natural frequency of the building during installation of the system, or when change in the structure of the building takes place, the mass cannot oscillate at the optimum vibration frequency when an earthquake occurs, thereby reducing the vibration-reducing effect.        (2) In an application of the system to a tall building, the mass typically has a weight of several tons. As a result, a relatively large space must be provided to allow for oscillation of the mass. This also necessitates the provision of a safety protective arrangement that is disposed around the space, and makes installation of the system in the building difficult.        (3) The system can absorb only horizontal vibration energy of a building.        